Encapsulation of Electrodes in Solid Media for use in conjunction with Fluid High Voltage Isolation

ABSTRACT

An inductively-coupled plasma source for a focused charged particle beam system includes a conductive shield that provides improved electrical isolation and reduced capacitive RF coupling and a dielectric fluid that insulates and cools the plasma chamber. The conductive shield may be enclosed in a solid dielectric media. The dielectric fluid may be circulated by a pump or not circulated by a pump. A heat tube can be used to cool the dielectric fluid.

This application is a continuation-in-part of U.S. patent applicationSer. No. 13/165,556, filed Jun. 21, 2011, and a continuation-in-part ofU.S. patent application Ser. No. 13/353,032, filed Jan. 18, 2012, whichis a continuation of U.S. patent application Ser. No. 13/182,925, filedJul. 14, 2011, which is a continuation of Ser. No. 12/982,606, filedDec. 30, 2010, which claims priority from U.S. Prov. App. 61/291,288,filed Dec. 30, 2009, all of which are hereby incorporated by reference.

TECHNICAL FIELD OF THE INVENTION

The present invention relates to inductively-coupled plasma ion sourcesand more specifically to the means of cooling the plasma sources whileproviding high voltage isolation.

BACKGROUND OF THE INVENTION

Inductively-coupled plasma (ICP) sources have advantages over othertypes of plasma sources when used with a focusing column to form afocused beam of charged particles, i.e., ions or electrons. Theinductively-coupled plasma source is capable of providing chargedparticles within a narrow energy range, which allows the particles to befocused to a small spot. ICP sources, such as the one described in U.S.Pat. No. 7,241,361, which is assigned to the assignee of the presentinvention, include a radio frequency (RF) antenna typically wrappedaround a ceramic plasma chamber. The RF antenna provides energy tomaintain the gas in an ionized state within the chamber.

The energy of ions used for ion beam processes is typically between 5keV and 50 keV, and most typically about 30 keV. Electron energy variesbetween about 500 eV to 5 keV for a scanning electron microscope systemto several hundred thousand electron volts for a transmission electronmicroscope system. The sample in a charged particle system is typicallymaintained at ground potential, with the source maintained at a largeelectrical potential, either positive or negative, depending on theparticles used to form the beam. Thus, the ion beam source is typicallymaintained at between 5 kV and 50 kV and the electron source istypically maintained at between 500 V and 5 kV. “High voltage” as usedherein means positive or negative voltage greater than about 500 V aboveor below ground potential. For the safety of operating personnel, it isnecessary to electrically isolate the high voltage components. Theelectrical isolation of the high voltage plasma creates several designproblems that are difficult to solve in light of other goals for aplasma source design.

One design difficulty occurs because gas must be brought into the highvoltage plasma chamber to replenish the gas as ions leave the plasma.The gas is typically stored at ground potential and well aboveatmospheric pressure. Gas pressure in a plasma chamber typically variesbetween about 10⁻³ mbar and about 1 mbar. The electrical potential ofthe gas must be brought to that of the high voltage plasma and thepressure of the gas must be decreased as the gas moves from the gassource into the plasma chamber. The gas must be brought into the chamberin a way that prevents a gas phase discharge, also known as arcing,which would damage the system.

Another design challenge is to place the radio frequency coils thatprovide power to the plasma as close as possible to the plasma toefficiently transfer power. Maintaining the coils at the same highpotential as the plasma, however, would typically require maintainingthe power supply for the coil at the high plasma potential, which wouldexcessively complicate the power supply design and greatly increase thecost. Inductively-coupled plasma ion sources may use a split Faradayshield to reduce capacitive coupling between the coil and the plasma.The split Faraday shield must be located between the plasma and thecoils and is typically well grounded. When the grounded Faraday shieldis located close to the dielectric plasma container, the large electricfield caused by the rapid change in potential would likely cause agas-phase discharge if any air or other low dielectric constant gas istrapped between the Faraday shield and the dielectric plasma chamber,which discharge could damage the source.

Also, the energy applied to the plasma chamber generates heat. While acompact plasma source is desirable for beam formation, the more compactand powerful the plasma source, the hotter the source would become andtherefore the greater the need to efficiently dissipate the heat. Thehigh voltage can also make cooling difficult, which can limit thedensity of the plasma used. These conflicting requirements make thedesign of an ICP source very challenging.

SUMMARY OF THE INVENTION

An object of the invention is to provide an improved plasma source andan improved charged particle system having a plasma charged particlebeam source.

This invention provides high voltage (HV) isolation and cooling of theinductively-coupled plasma source for a charged particle beam system. Inone preferred embodiment, the plasma source is surrounded by a Faradayshield substantially encapsulated in a solid dielectric media thatprevents gaseous high voltage breakdown at the surface of the shield. Inanother embodiment, the plasma source is surrounded at least in part bya static fluid that provides HV isolation. The term “static fluid” asused herein means a fluid that is not actively pumped.

The foregoing has outlined rather broadly the features and technicaladvantages of the present invention in order that the detaileddescription of the invention that follows may be better understood.Additional features and advantages of the invention will be describedhereinafter. It should be appreciated by those skilled in the art thatthe conception and specific embodiments disclosed may be readilyutilized as a basis for modifying or designing other structures forcarrying out the same purposes of the present invention. It should alsobe realized by those skilled in the art that such equivalentconstructions do not depart from the spirit and scope of the inventionas set forth in the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more thorough understanding of the present invention, andadvantages thereof, reference is now made to the following descriptionstaken in conjunction with the accompanying drawings, in which:

FIG. 1 shows a longitudinal cross-sectional schematic view of a plasmasource that uses a Faraday shield for reduced coupling and an insulatingfluid for high voltage isolation and cooling.

FIG. 2 shows a transverse cross-sectional schematic view of the plasmasource of FIG. 1.

FIG. 3 shows charged particle beam system that uses a plasma sourcewhich uses an insulating fluid for cooling and high voltage isolation.

FIG. 4 shows a longitudinal half-sectional schematic view of a plasmasource which uses a static fluid for high voltage isolation and activecooling elements.

FIG. 5 shows a longitudinal half-sectional schematic view of a plasmasource that uses a Faraday shield substantially encapsulated in a soliddielectric media for improved electrical isolation and reduced RFcoupling.

FIG. 6A shows a cross-sectional schematic view of a plasma source withintegrated heat pipe cooling.

FIG. 6B shows a cross-sectional schematic view of a plasma source withintegrated heat pipe cooling, displaying one heat pipe.

FIG. 6C shows a top view of a plasma source with integrated heat pipecooling, displaying an example configuration of several heat pipesdistributed around the perimeter of the plasma source.

FIG. 6D shows a side view of a plasma source with integrated heat pipecooling, displaying an example heat pipe configuration.

FIG. 7 shows a front view of a plasma source with a plasma chamberbonded to a split Faraday shield surrounded by an encapsulant.

FIG. 8 shows a partial cross section of the plasma source of FIG. 7.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Designing a plasma source typically requires many tradeoffs to meetconflicting design requirements. Embodiments of the invention canprovide excellent coupling between the RF coil and the plasma, efficientcooling of the plasma chamber, excellent capacitive screening, and highvoltage isolation of the plasma source all of which can produce aninductively-coupled plasma that is dense, quiescent, and at highpotential.

In some embodiments, expelling air from regions with strong electricfields and filling those volumes with a liquid or other high dielectricconstant fluid provides a system designer the opportunity to make designchoices with regard to the source configuration that would be otherwiseunavailable.

The description below describes a plasma source for a focused ion beamsystem, but a plasma source of the present invention can be used for anelectron beam system, or other system. As used herein, a “fluid” cancomprise a liquid or a gas.

FIG. 1 shows a stylized longitudinal cross-sectional view of a plasmasource 100. The plasma source 100 includes a dielectric plasma chamber102 having an interior wall 104 and an exterior wall 106. Plasma chamber102 rests on a conductive base plate 110. Plasma 112 is maintainedwithin the plasma chamber 102. Extraction optics 114 extract chargedparticles, ion or electrons depending on the application, from plasma112 through an opening 116 in plasma chamber 102 and opening 118 in baseplate 110. A dielectric outer shell 120, preferably of ceramic orplastic material that transmits radio frequency energy with minimalloss, is concentric with plasma chamber 102 and defines a space 122between outer shell 120 and plasma chamber outer wall 106. A splitFaraday shield 134 is located in space 122 and is typically concentricwith the plasma chamber 102. A pump 124 pumps a cooling fluid 126 from areservoir/chiller 127 to space 122 through cooling fluid inlets 128 andexit through exit 132, cooling plasma chamber 102 by thermal transferfrom outer wall 106.

The split Faraday shield 134 is typically fixed to ground potential andtherefore the electrical potential drops rapidly between the plasmaregion and the split Faraday shield, thus materials between the plasmaregion and the split Faraday shield must have sufficiently largedielectric strength to resist arcing. The cooling fluid can be chosen tohave a sufficiently high dielectric constant compared to the material ofceramic housing 102 so that the voltage drop across the fluid issufficiently low to prevent dielectric breakdown at the operatingvoltage. A liquid coolant is chosen to be free of gaseous bubbles orother impurities which could present the opportunity for fieldenhancement and gaseous electric discharge. The cooling fluid can alsobe chosen to be slightly conductive in which case the fluid volume willbe substantially free of electric fields and substantially all of thevoltage drop will take place in the plasma chamber 102. The coolingfluid should also have sufficient heat capacity to prevent the plasmachamber 102 from overheating without requiring a large fluid flow thatrequires a large pump that would consume excessive power. The plasmachamber outer wall 106 is typically maintained at a temperature of lessthan about 50° C.

The fluid preferably comprises a liquid, such as water or Fluorinert™FC-40, an electrically insulating, stable fluorocarbon-based fluid soldcommercially by 3M Company, St. Paul, Minn. Other electricallyinsulating fluids, such as mineral oil, may be used. Water, such asdistilled water or tap water, may be used. An insulating gas, such assulfur hexafluoride, may also be used. A cooling pump typically pumpsthe cooling liquid at a rate of between 10 gal/hour and 50 gal/hour fromreservoir/chiller 127. Fluid 126 returns from exit 132 tochiller/reservoir 127 via a return conduit 133. Alternately, the coolingfluid can be static liquid that is not mechanically pumped, allowing forsignificant power savings. Water at room temperature has a dielectricconstant of about 80, whereas the ceramic material of the plasma chamberhas a dielectric constant of about 9, which results in most of thevoltage drop occurring in the ceramic. A preferred insulating fluid hasa dielectric constant preferably greater than that of the dielectricmaterial of which the plasma chamber is made. In some embodiments, theinsulating fluid has a dielectric constant greater than 5, morepreferably greater than 10, even more preferably greater than 20, andmost preferably greater than or equal to about 40.

In a typical embodiment, reservoir/chiller 127 cools the cooling fluidto about 20° C. before the fluid is recirculated by pump 124. Thecooling fluid partly surrounds the plasma chamber and the coolant flowslongitudinally along the plasma chamber from bottom to top. For clarity,FIG. 1 shows cooling fluid entering space 122 on two sides at the bottomof plasma chamber 102 and exiting space 122 one on side at the top ofchamber 102. Skilled persons will understand that suitable inlets,outlets, and baffles may be used to ensure an even fluid flow around allsides of the plasma chamber 102.

A Faraday shield 134 passes the radio frequency energy from RF coils 136to energize the plasma while reducing the capacitive coupling betweenradio frequency coils 136 and plasma 112. In some embodiments, theFaraday shield 134 is protected from corrosion and physical damage bybeing substantially encapsulated in a solid dielectric media, such asceramic, glass, resin, or polymer, to eliminate unwanted fluid incontact with the Faraday shield and to eliminate high voltage discharge.RF coils 136 may be hollow and cooled by flow of a fluid coolant throughthe internal passages 137 in the coils. The plasma chamber coolantsystem may also pump fluid coolant through the coils, or the coils canhave an independent cooling system.

Faraday shield 134 can be positioned such that cooling fluid 126 flowson both sides of the shield 134. In some embodiments, the shield can bepositioned against the plasma chamber outer wall 106 or onto the insidewall of shell 120. For example, the shield can comprise a metallic layerpainted or otherwise deposited on outer plasma chamber wall 106 orinside shell wall 120. Faraday shield 134 is electrically grounded. Inone embodiment, shield 134 comprises a slotted metal cylinder that isgrounded by trapping a tab 138 of the Faraday shield between a portionof outer shell 120 and base plate 110, thereby ensuring a solid groundcontact.

The gas from which the plasma is produced must be brought from groundpotential to the plasma potential along the path between the tank 150and the plasma. In a preferred embodiment, most of the voltage changeoccurs where the gas pressure is relatively high and resistant toarcing.

Gas is provided to plasma chamber 102 from a gas source, such as a tank150. Tank 150 is typically maintained at ground potential and containsthe gas at a high pressure. A regulator 152 reduces the pressure of thegas leaving the tank entering a conduit 154. An optional adjustablevalve 156 further reduces the pressure in the gas line or closes theconduit completely when the source is not in use. A flow restrictor,such as a capillary 158, further reduces the gas pressure before the gasreaches plasma chamber 106. Restrictor 158 provides a desired gasconductance between the gas line and the interior of plasma chamber 102.Restrictor 158 is preferably in electrical contact with plasma 112 andso is at the plasma potential. In other embodiments, the flowrestriction can have an electrical bias applied from a voltage sourceother than the plasma. An insulating shield 160 surrounds capillary 158and a grounded metallic collar 162 at the end of insulating shield 160ensures that the electrical potential of the gas is zero at thatposition. Thus, the entire electrical potential change from ground tothe plasma voltage occurs within insulating shield 160 in which the gasis at a relatively high pressure and therefore resistant to arcing.

In one example embodiment without a valve 156, regulator 152 reduces thepressure of the gas leaving the supply tank from 150 psig to 5 psig. Thegas pressure remains at 5 psig until the gas reaches capillary 158, andwhich point the gas pressure drops to the plasma chamber pressure of,for example, 0.1 Ton. Insulating shield 160 preferably has sufficientlength to keep the field sufficiently low to prevent a damagingdischarge. Insulating shield 160 is typically about at least about 5 mmlong, and more typically between about 30 mm and 60 mm. For example, ifthe plasma is maintained at 30 kV, the electric field within a 10 mmshield is about 3 kV/mm, which is sufficiently low to prevent asustained discharged in most applications. Skilled persons willunderstand that the local electric field will be a function of thegeometry and that initial low current discharges may occur to reach astatic charge equilibrium within insulating shield 160. In someembodiments, valve 156 may reduce the gas pressure further before thegas reaches the final restrictor before the plasma. Instead of acapillary, the flow restrictor could be a valve, such as a leak valve.Any type of gas source could be used. For example, the gas source maycomprise a liquid or solid material that is heated to produce gas at asufficient rate to supply the plasma. The different output pressures ofthe different gas sources may require different components to reduce thepressure to that required in the plasma chamber.

FIG. 2 shows a transverse cross-sectional view of plasma source 100 inFIG. 1. FIG. 2 shows that the outer wall 106 of plasma chamber 102 iscorrugated, that is, it is composed of a series of ridges 202 andvalleys 204. The Faraday shield 134 is positioned against the ridges202, defining passages 206 for the cooling fluid to flow between thevalleys 204 and the shield 134. In the embodiment shown in FIG. 2, theFaraday shield 134 comprises a metal sleeve that slips over plasmachamber outer wall 106. A portion of the metal sleeve is then bentoutward at the bottom to form grounding tab 138 (FIG. 1), which istrapped between plasma chamber 102 and ground plate 110. Cooling fluid126 flows through the space 122 which is bounded by the plasma chamberouter wall 106 and the shell 120. The Faraday shield is “split”, thatis, there are longitudinal slots in the shield, which allow forinductive coupling between the RF antenna and the plasma 112. In analternative embodiment, the outer wall 106 may be smooth and the Faradayshield formed with corrugations. Alternatively, neither the wall 106 northe faraday shield may be corrugated.

FIG. 3 shows a charged particle beam that uses the plasma source ofFIG. 1. At the top of the ion column, an inductively-coupled plasma(ICP) ion source 302 is mounted, comprising an electromagnetic enclosure304, a source chamber 306, and an induction coil 308, which includes oneor more windings of a conductive material. In the embodiment shown inFIG. 3, a coolant reservoir and chiller 390 provides coolant to a pump391, which provides coolant by conduit 392 to a coolant region aroundsource chamber 306. The coolant then flows back to coolant reservoir andchiller 390 through a return conduit 393. In an alternative embodiment,the coolant region around the source chamber 306 contains a staticliquid for high voltage isolation. In such embodiments.reservoir/chiller 390 and coolant pump 391 can be eliminated or can beused to circulate a cooling fluid that does not enter a high voltageregion. In yet another embodiment, liquid in the plasma source 302 iscooled by one or more heat pipes, as described in more detail below.

An RF power supply 340 is connected to a match box 341 by an RF coaxialcable 342. The match box 341 is connected to the induction coil 308 bycoil leg extentions 343. The induction coil 308 is mounted coaxiallywith the source chamber 306. To reduce capacitive coupling between theinduction coil 308 and the plasma generated within the source chamber306, a split Faraday shield (not shown) may optionally be mountedcoaxially with the source chamber 306 and inside the induction coil 308.When a split Faraday shield is used in the ICP ion source 302, the highvoltage (typically several hundred to a few thousand volts) across theinduction coil 308 will have minimal effect on the energies of the ionsextracted from the bottom of the ICP ion source 302 into the ion column.This will result in smaller beam energy spreads, reducing the chromaticaberration in the focused charged particle beam at or near the substratesurface.

The presence of a plasma within the source chamber 306 may be detectedusing the light emitted by the plasma and collected by the source-facingend of optic fiber 344, and transmitted through optic fiber 344 to aplasma light detection unit 345. An electrical signal generated by theplasma light detection unit 345 is conducted through cable 346 to aprogrammable logic controller (PLC) 347. The plasma on/off signalgenerated by the plasma light detection unit 345 then passes from thePLC 347 through cable or data bus 348 to the plasma source controller351 executing plasma source control software. Signals from the plasmasource controller 351 may then pass through cable or data bus 352 to thefocused ion beam (FIB) system controller 353. The FIB system controller353 may communicate via the Internet 354 to a remote server 355. Thesedetails of the interconnections of the various components of the FIBsystem control are for exemplary purposes only. Other controlconfigurations are possible as is familiar to those skilled in the art.

Gas is provided to the source chamber 306 by inlet gas line 320 whichleads to inlet restrictor 328, which leads to the interior of the sourcechamber 306. Restrictor 328 is maintained at an electrical potentialcloser to the potential of the plasma in chamber 306 than to thepotential of the gas source 310 and regulator 332 so that the voltagedrop occurs primarily across gas of higher pressure. Insulating shield329 insulates the gas line upstream of restrictor 328 and is terminatedwith a grounded collar 331.

A gas supply system 310 for the ICP source comprises a gas supply 330, ahigh purity gas regulator 332, and a needle (regulating) valve 334. Thegas supply 330 may comprise a standard gas bottle with one or morestages of flow regulation, as would be the case for helium, oxygen,xenon or argon feed gases, for example. Alternatively, for gases derivedfrom compounds which are solid or liquid at room temperature, gas supply330 may comprise a heated reservoir. Other types of gas supplies 330 arealso possible. The particular choice of gas supply 330 configuration isa function of the type of gas to be supplied to the ICP source. Gas fromsupply 330 passes through high purity gas regulator 332, which maycomprise one or more stages of purification and pressure reduction. Thepurified gas emerging from high purity gas regulator 332 passes throughan optional needle valve 334. Gas emerging from optional needle valve334 passes through a hose 336 to an optional second needle valve 338,mounted in close proximity to the ICP source. Gases emerging from needlevalve 338 pass through inlet gas line 320, which connects throughrestriction 328 to the top of the source chamber 306.

At the bottom of the ICP source 302, a source electrode 357 serves aspart of the ion beam extraction optics, working in conjunction with theextractor electrode 358 and the condenser 359. A plasma igniter 360 isconnected to a source electrode (not shown), enabling the starting ofthe plasma in the source enclosure 306. Other known means of ignitingthe plasma can also be used. Details of the operation of the ICP sourceare provided in U.S. Pat. No. 7,241,361, issued Jul. 10, 2007,incorporated by reference herein. The source electrode 357 is biasedthrough the igniter 360 to a high voltage by beam voltage power supply(PS) 361. The voltage on the source electrode 357 determines potentialof the plasma and therefore the energy of the charged particles reachingthe substrate surface in the case of singly-ionized atomic or molecularion species or electrons. Doubly-ionized ion species will have twice thekinetic energy. The extractor electrode 358 is biased by extractor powersupply 363, while the condenser 359 is biased by condenser power supply362. The combined operation of the source electrode 357, the extractor358, and the condenser 359 serves to extract and focus ions emergingfrom the ICP source 302 into a beam which passes to the beam acceptanceaperture 364. The beam acceptance aperture 364 is mechanicallypositioned within the ion column by the beam acceptance apertureactuator 365, under control of the FIB system controller 353. Typicalvoltage settings may be roughly +30 kV for power supply 361, roughly 15kV for power supply 362 and roughly 15 kV for power supply 363.

The ion column illustrated in FIG. 3 shows two electrostatic einzellenses 366 and 367, used to form a highly demagnified (roughly 1/125×)image of the virtual source in the ICP source 302 at or near the surfaceof substrate 368, mounted on stage 369 controlled by a sample stagecontroller 337. The first einzel lens, 366, referred to as “lens 1” or“L1,” is located directly below the beam acceptance aperture 364 andcomprises three electrodes with the first and third electrodes typicallybeing grounded (at 0 V), while the voltage of the center electrode 370is controlled by lens 1 (L1) power supply (PS) 371. The lens 1 powersupply 371 is controlled by the FIB system controller 353.

Between the first einzel lens 366 and the second einzel lens 367 in theion column, a beam defining aperture assembly 372 is mounted, comprisingone or more beam defining apertures (three apertures are shown in FIG.1). Typically, the beam defining aperture assembly 372 would comprise anumber of circular apertures with differing diameter openings, where anyone of which could be positioned on the optical axis to enable controlof the beam current and half-angle at the substrate surface.Alternatively, two or more of the apertures in the beam definingaperture assembly 372 may be the same, thereby providing redundancy toenable the time between aperture maintenance cycles to be extended. Bycontrolling the beam half-angle, together with corresponding adjustmentsof the lenses, the beam current and diameter of the focused ion beam ator near the substrate surface may be selected, based on the spatialresolution requirements of the milling or imaging operations to beperformed. The particular aperture to be used (and thus the beamhalf-angle at the substrate) is determined by mechanical positioning ofthe desired aperture in the beam defining aperture assembly 372 on theoptical axis of the column by means of the beam defining aperture (BDA)actuator 373, controlled by the FIB system controller 950.

Beneath the beam defining aperture assembly 372, the second einzel lens367, referred to as “lens 2” or “L2,” is shown. The first and thirdelectrodes are typically grounded (0 V), while the voltage of the centerelectrode 374 is controlled by lens 2 (L2) power supply (PS) 375. Thelens 2 power supply 375 is controlled by the FIB system controller 353.A column/chamber isolation valve 376 is positioned somewhere between thesource 302 and the sample chamber 378. Isolation valve 376 enables thevacuum in the ion column vacuum chamber 377 to be maintained at highlevels, even if the vacuum level in the sample chamber 378 is adverselyaffected by sample outgassing, during sample introduction and removal,or for some other reason. A source/chamber turbopump 379 is configuredto pump the sample chamber 378 through a pumping line 380. Turbopump 379also pumps the ion column enclosure 377 through pumping line 381.

The details of the FIB system illustrated in FIG. 3 are for exemplarypurposes only—many other FIB system configurations are capable ofimplementing a multiple mode embodiment of the present invention formilling and imaging. For example, the ion column illustrated in FIG. 3shows two electrostatic einzel lenses. The ion column may alternativelybe implemented using a single electrostatic einzel lens, or more thantwo electrostatic lenses. Other embodiments might include magneticlenses or combinations of two or more electrostatic or magneticquadrupoles in strong-focusing configurations. For the purposes of thisembodiment of the present invention, it is preferred that the ion columnforms a highly demagnified image of the virtual source (in the ICPsource 302) at or near the surface of the substrate 368. Details ofthese possible demagnification methods are familiar to those skilled inthe art.

FIG. 4 shows a half-sectional view of another embodiment of a plasmasource 400 that includes a dielectric plasma chamber 402 having an innerwall 404 and an outer wall 406. FIG. 4 shows a static fluid 408positioned in a cavity 410 between the antenna coils 436 and the outerwall 406 of the plasma chamber and a shell 416. Static fluid maycomprise a liquid, such as Fluorinert, oil, or distilled water, or gas,such as sulfur hexafluoride. A split Faraday shield 412 is alsopositioned between shell 416 and outer wall 406. Faraday shield 412 canbe positioned against shell 416 as shown, against outer wall 406, oraway from both walls and immersed in the static fluid 408. Whenpositioned between a grounded split Faraday shield 412 and the outerwall 406, fluid 408 provides part of the high voltage isolation of theplasma chamber. Static fluid 408 is preferably not circulated outside ofthe source 400 by an external pump, although static fluid 408 may moveinternally by convection within. One or more optional cooling devices414 assist in cooling the plasma chamber 402. Cooling devices 414 maycomprise cooling loops that encircle the plasma chamber and throughwhich a fluid circulates. Because cooling devices 414 are positionedoutside of the Faraday shield, which is at ground potential, thesedevices do not perform any voltage isolation and hence any type ofcooling fluid may be used in cooling devices 414. Alternatively, coolingdevices 414 may comprise one or more thermoelectric coolers, such asPeltier effect coolers. The RF coils 436 may be hollow and cooled byflow of a coolant through the internal passages 437 in the coils.

FIG. 5 shows a half-sectional view of a plasma source 500 of anotherembodiment of the invention. FIG. 5 shows the Faraday shield 512substantially encapsulated in a solid dielectric media 516, which ispositioned between the RF coils 536 and the plasma chamber outer wall506. Solid dielectric media 516 can comprise, for example, a ceramicmaterial such as alumina or quartz, a resin, or an epoxy encapsulantsuch as Stycast W-19 or Stycast 2762, sold commercially by Emerson &Cumming Specialty Polymers, Billerica, Mass. An optional gap between thedielectric media 516 and outer wall 506 defines a fluid cavity 510,which can be filled with a fluid, such as Fluorinert, distilled water,oil (for example mineral oil), or sulfur hexafluoride. Non-encapsulatedportions 538 of the Faraday shield 512 are available to form groundingconnections. In some embodiments, fluid 508 is pumped through the fluidcavity 510 and then through a cooler, using a system similar to thesystem shown in FIG. 1. In other embodiments, fluid 508 is not pumpedoutside the source and remains within fluid cavity 510. The RF coils 536may be hollow and cooled by flow of a coolant through the internalpassages 537 in the coils.

In some embodiments, dielectric media 516 can be positioned againstouter wall 506 without an intervening fluid. To avoid an air gap in suchembodiments, dielectric media 516 should fit tightly against outer wall506. Air gaps can also be avoided by providing a flowable material tofill displace any air between outer wall 506 and dielectric media 506.The flowable media can be, for example, a high dielectric constantgrease or gel. The flowable material can remain liquid or may solidifyafter positioning the dielectric media relative to the plasma chamber.In some embodiments, the dielectric media can comprise a flowable mediumthat hardens or remains liquid. For example, a flowable, hardenablematerial may be applied to outer wall 506 and/or to Faraday shield 512before Faraday shield 512 is slipped over outer wall 506, so that theFaraday shield is positioned around outer wall 506, with the flowablemedium filling any gap between Faraday shield 512 and the outer wall506. The flowable medium may also coat the Faraday shield on the sideopposite to outer wall 506, thereby preventing contact between anycooling fluid and the Faraday shield. In some embodiments, the Faradayshield can be molded into the wall of plasma chamber 502.

FIG. 6A through FIG. 6D show multiple views of another embodiment of aplasma source 600 with integrated heat pipe cooling. The plasma source600 includes a dielectric plasma chamber 604 having an interior wall 628and an exterior wall 626. FIG. 6A shows a cross-sectional schematic viewof the embodiment of plasma source 600 which incorporates a preferredheat pipe cooling device. See cross-section cut line B-B of FIG. 6C. A“heat pipe” is a heat-transfer device that utilizes phase transition toefficiently transfer heat. In this embodiment, a static fluid coolant602 surrounds the plasma chamber 604 having one or more heat pipes 606integrated into the upper portion of the coolant jacket 608. The coolant602 is evaporated by heat from the plasma chamber 604 creating coolantvapor 610 which rises toward the cooling fins 612. Heat from the coolantvapor 610 is dissipated through the cooling fins 612 and transferredinto the surrounding air causing the coolant vapor to cool. As thecoolant vapor cools, it condenses and flows back into coolant jacket608. Alternately, the liquid inside of the heat pipe 606 may be separatefrom the liquid in the cooling jacket 608, having theevaporation-condensation cycle self-contained within the heat pipe.

Preferably, multiple heat pipes are integrated into the upper portion ofthe coolant jacket 608 to provide increased heat dissipation capability.The coolant 602 is positioned in the coolant jacket 608 which ispositioned between the antenna coils 620 and the outer wall 626 of theplasma chamber, preferably positioned between a split Faraday shield 624and the outer wall 626. Alternately, the split Faraday shield may besubstantially encapsulated in a solid dielectric media. When positionedbetween a grounded split Faraday shield 624 and the outer wall 626,liquid 602 provides part of the high voltage isolation of the plasmachamber. Static liquid coolant 602 is not circulated outside of thesource 600 by an external pump, although static liquid coolant 602 maymove internally by convection and also by the gravity flow of thecondensing coolant. In some embodiments, liquid coolant carries heataway from wall 626 by convection and without a phase change, with thehot liquid rising, being cooled, for example, by cooling fin 612, andflowing back into cooling jacket 608. Coolant can flow in contact withouter wall 626, or it can flow in cooling channels outside of outer wall626. The RF coils 620 may be hollow and cooled by flow of a coolantthrough the internal passages 622 in the coils. Gas enters the plasmachamber 604 through gas inlet 614, and charged particles are pulled fromthe plasma chamber 604 by an extractor electrode 632.

FIG. 6B shows a cross-sectional view through cut line A-A of the plasmasource 600 in FIG. 6A, illustrating one heat pipe. The source end of theheat pipe 606 is connected to the coolant jacket 608 which surrounds theplasma chamber 604. Static liquid coolant 602 occupies the coolantjacket space. The opposite end of the heat pipe 606 is connected to thecooling fin mount 618. Liquid coolant is referred to as static becauseit is not actively pumped, although it will be understood that theliquid may move due to thermal gradients in the liquid.

FIG. 6C shows a top view of the plasma source 600 with an exampleconfiguration of integrated heat pipes. In this embodiment, eight heatpipes 606 are integrated radially to the plasma source and located nearthe top of the plasma source. Each heat pipe 606 has a cooling fin mount618 attached to the outward end of the heat pipe. One or more coolingfins 612 are connected to each cooling fin mount 618.

FIG. 6D shows a side view of the plasma source 600 in FIG. 6C with oneof the eight heat pipes, heat pipe 634, cut away to further illustratethe cooling fin and heat pipe arrangement. For clarity, only theforeground heat pipes are depicted in this diagram. Heat pipes 606 areintegrated radially to the plasma source and located in the upperportion of the plasma source. Each heat pipe 606 has a cooling fin mount618 with one or more cooling fins 612 attached.

FIG. 7 shows a front view of a portion of a plasma source 700 includinga dielectric structure 702 having an interior cavity (not visible) forcontaining a plasma. That is, the dielectric structure 702 forms thewalls of the plasma chamber. A split Faraday shield 708 is positionedsuch that the shield is in contact with, and preferably intimatelybonded to, dielectric structure 702. Preferably, Faraday shield 708 isconfigured such that there are substantially no voids (that is, emptyspaces that could be filled by air, cooling fluid, or any other fluid)between the shield and the dielectric structure 702. The absence ofvoids around the dielectric structure 702 ensures that no high voltagearc discharge can occur. Substantially no voids means that any voidsthat are present are sufficiently small to prevent damaging arcing.

The shield 708 can be for example, similar to the shield described inUS. patent application Ser. No. 13/353,032, which is assigned to theassignee of the present invention. An encapsulant 710 is applied tosurround split Faraday shield 708. For illustration, FIG. 7 shows theFaraday shield 708 visible through a translucent encapsulant 710. SplitFaraday shield 708 has gaps 722 to reduce eddy currents that drainenergy from the RF coils. The encapsulant 710 preferably contacts andadheres to the regions of the dielectric structure 702 in the gaps 722and, in some embodiments, in other regions that are not covered byshield 708. There are preferably substantially no voids between theencapsulant and the dielectric structure in regions where theencapsulant contacts the dielectric structure. In other words, there arepreferably no voids between the encapsulant and the dielectric structureregardless of whether potions of the shield are between the encapsulantand the dielectric structure. A portion of the split-Faraday shield 708,such as regions 712, extends from beneath the encapsulant 710 in orderto provide a means of electrical connection to the shield. Theextensions may also be, for example, in the form of tabs. Instead ofregions of the Faraday shield extending from the encapsulant, anelectrical contact could be made through a gap in the encapsulant or aconductor could extend out of the encapsulant from the Faraday shield.

The encapsulant 710 is preferably a thin, leak-proof, dielectricmaterial that adheres to and protects the covered portion of the shield708 and of the dielectric structure 702. The encapsulant is notelectrically conductive so that no eddy currents can be supported withinthe media. Encapsulant 710 should be thin to increase heat conductancefrom structure 702. The thickness of a preferred encapsulant is lessthan 10 mm, more preferably less than 5 mm, and even more preferablyless than 3 mm. Encapsulant 710 is preferably highly thermallyconductive in order to present the lowest possible thermal barrier sothe plasma chamber may be efficiently cooled by different coolingmethods, such as the ones described in previous embodiments.Furthermore, the encapsulant 710 is preferably non-porous so that thereis no fluid contact with the split-Faraday shield where it is surroundedby the encapsulant 710. Suitable materials for the encapsulant 710 mayinclude, but are not limited to epoxy, enamel, and glass frit.

Using a split-Faraday shield 708 in contact with dielectric structure702 and configured so that there is no air between the Faraday shieldand the dielectric structure, as well as using an encapsulant thatprotects the shield and allows no air between the encapsulant and theFaraday shield, prevents air and cooling liquid from coming in to thehigh DC voltage region between the plasma chamber and the Faradayshield, thereby simplifying the design of the system.

FIG. 8 shows a partial sectional view of the embodiment shown in FIG. 7.The dielectric structure 702 defines an inner wall 804 and an outer wall806 of a plasma chamber 808. A plasma is maintained within plasmachamber 808. Split Faraday shield 708 is positioned such that it is incontact with outer wall 806. Encapsulant 710 is applied to a portion ofouter wall 806 such that the encapsulant is well adhered to the Faradayshield 708 and to the portions of the outer wall 806 that remain exposedby the slits in the split Faraday shield, thereby excluding any air orcooling fluid between the Faraday shield and the outer wall 806. Regions712 of the split Faraday shield extend from beneath the encapsulant 710,either above the encapsulant, below the encapsulant, or both above andbelow the encapsulant. Cooling methods, such as the ones described byprevious embodiments, may be supplied in the space 832 between theencapsulant 710 and a dielectric outer shell 834, which is preferablymade of ceramic or plastic material that transmits radio frequencyenergy with minimal loss. The RF coils 812 may be hollow and cooled byflow of a coolant through the internal passages in the coils.

Materials and structures described in one embodiment or described aspart of the prior art may be used in other embodiments. Although thepresent invention and its advantages have been described in detail, itshould be understood that various changes, substitutions and alterationscan be made to the embodiments described herein without departing fromthe spirit and scope of the invention as defined by the appended claims.Moreover, the scope of the present application is not intended to belimited to the particular embodiments of the process, machine,manufacture, composition of matter, means, methods and steps describedin the specification. As one of ordinary skill in the art will readilyappreciate from the disclosure of the present invention, processes,machines, manufacture, compositions of matter, means, methods, or steps,presently existing or later to be developed that perform substantiallythe same function or achieve substantially the same result as thecorresponding embodiments described herein may be utilized according tothe present invention. Accordingly, the appended claims are intended toinclude within their scope such processes, machines, manufacture,compositions of matter, means, methods, or steps.

1-21. (canceled)
 22. A charged particle beam system, comprising: aplasma source having: a plasma chamber having a wall composed of adielectric material, the wall having an interior surface and an exteriorsurface; a conductor coiled at least one time around the plasma chamber;a shield composed of an electrically conductive material andsubstantially encapsulated in a dielectric media, the conductive shieldpositioned between the plasma chamber and the conductor coiled aroundthe plasma chamber; and a source electrode for electrically biasing theplasma to a high voltage; and one or more focusing lenses for focusingcharged particles from the plasma source onto a sample.
 23. The chargedparticle beam system of claim 22 in which the shield is positioned onthe exterior surface of the plasma chamber.
 24. The charged particlebeam system of claim 23 in which there are substantially no voidsbetween the conductive material of the shield and the exterior surfaceof the plasma chamber.
 25. The charged particle beam system of claim 23in which the shield includes gaps for passing an inductive field to theplasma chamber and in which the dielectric encapsulant contacts theexterior surface of the plasma chamber wall between the gaps in theconductive material.
 26. The charged particle beam system of claim 22 inwhich the dielectric encapsulant comprises an epoxy, enamel, a glassfrit, a resin, or a polymer.
 27. The charged particle beam system ofclaim 22 further comprising a fluid contacting at least a portion of thedielectric media.
 28. The charged particle beam system of claim 27 inwhich the fluid is positioned between the dielectric encapsulant and theconductor coiled around the plasma chamber.
 29. The charged particlebeam system of claim 27 in which the fluid is positioned between theexterior surface of the plasma chamber and the dielectric encapsulant.30. The charged particle beam system as in claim 27 in which the fluidis not actively pumped.
 31. The charged particle beam system of claim 23in which a non-encapsulated portion of the shield is exposed for makingelectrical contact.
 32. The charged particle beam system of claim 23 inwhich a material is provided to displace any voids between the exteriorsurface of the plasma chamber wall and the dielectric media.
 33. Thecharged particle beam system of claim 32 in which the material providedto displace any gaps between the exterior surface of the wall and thedielectric media comprises a liquid or a liquid that subsequentlyhardens after being applied.
 34. A plasma source for a charged particlebeam system comprising: a plasma chamber having a wall with an interiorsurface and an exterior surface; a conductor for providing radiofrequency energy to the plasma chamber; a conductive shieldsubstantially encapsulated in a dielectric media, the conductive shieldpositioned between the conductor and the exterior surface of the plasmachamber; and a fluid positioned between the conductive shield and theconductor.
 35. The plasma source of claim 34 in which the fluid iscooled by a cooling system.
 36. The plasma source of claim 34 in whichthe fluid comprises water or a fluorine compound.
 37. The plasma sourceof claim 34 in which the fluid is positioned between the exteriorsurface of the plasma chamber and the dielectric media encapsulating theconductive shield.
 38. The plasma source of claim 34 in which the fluidis positioned between the exterior surface of the plasma chamber and thedielectric media encapsulating the conductive shield.
 39. A method ofproviding high voltage isolation to a plasma source of a chargedparticle beam system, comprising: providing a plasma chamber; providinga conductor coiled at least one time around the plasma chamber;providing a conductive shield positioned between the plasma chamber andthe conductor; substantially encapsulating the conductive shield in asolid dielectric media; and providing a source electrode forelectrically biasing the plasma to a high voltage.
 40. The method ofclaim 39 further comprising providing a cooling fluid contacting atleast a portion of the solid dielectric media.
 41. The method of claim39 in which the cooling fluid is positioned between the plasma chamberand the dielectric media encapsulating the conductive shield.
 42. Themethod of claim 39 in which the cooling fluid is positioned between thedielectric media encapsulating the conductive shield and the conductorcoiled around the plasma chamber.
 43. The method of claim 39 furthercomprising pumping the cooling fluid to cool the plasma chamber.